A major stated research priority of the National Eye Institute is "to identify the genes involved in retinal degenerative diseases". Although numerous genes causing retinal degeneration have been discovered, many remain to be identified, and novel approaches to the identification of additional retinal degeneration genes are needed. The goal of this project is the identification of genes that cause human retinal degeneration, specifically genes causing a syndromic form of photoreceptor degeneration known as Bardet- Biedl syndrome (BBS), as well as autosomal recessive retinitis pigmentosa (ARRP). BBS is a genetically heterogeneous disorder for which eleven genes have been identified to date, and for which there is strong evidence that multiple additional genes remain to be discovered. Similarly, the known ARRP genes account for less than half of all cases, a finding that indicates that numerous retinal disease genes remain to be discovered. Historically, the identification of disease genes has relied on genetic mapping and positional cloning using large affected families. The lack of large families for many diseases makes it necessary to use alternative strategies. In this application, we propose to use single nucleotide polymorphism (SNP) genotyping of small consanguineous families to identify candidate regions of homozygosity in combination with comparative genomic data and novel eye gene expression data to identify BBS genes. We present preliminary data showing the effectiveness of this approach. In addition, we will use a novel highly cost effective strategy to screen candidate genes for mutations in ARRP patients. In addition to disease gene discovery, we propose to further develop and validate methods for the functional analysis of retinal disease candidate genes using the zebrafish model system. Analysis of function is an important step in the verification of candidate genes as a cause of retinal diseases. The development, validation and utilization of a high throughput assay to verify disease causation is an important component of the overall goal to identify new retinal disease genes.